1. Field of the Invention
The present invention relates generally to data storage and in particular to a non-volatile data storage unit which may be programmed to a predetermined value, erased and read and a method of controlling the data storage unit.
2. Background Art
In many integrated circuit devices, it is desirable to have the capability of storing certain parameters relating to the operation of the integrated circuit. By way of example, sometimes an integrated circuit is implemented so that it can be used in different operating modes. The circuit can be configured at a fabrication facility to permanently operate in only one mode, depending upon the requirements of a particular user. This can be achieved by modifying the metallization layer of the integrated circuit so that the desired operating mode is achieved.
This approach has one advantage in that the change in metallization is permanent and will not be affected by loss of operating power. However, this advantage is offset by many disadvantages. A major disadvantage is that further changes in the stored operating parameters cannot be made once the metallization has been completed. This is particularly disadvantageous where the value of the stored parameters is dependent upon the characteristics of the integrated circuit which frequently cannot be ascertained until the metallization has been completed. In addition, once the integrated circuit has been packaged, it is frequently impossible to ascertain the value of the stored parameter.
The present invention provides the capability of storing operating parameters in an integrated circuit which can be altered at any time after the fabrication process. Once a parameter has been stored, the parameter is retained even in the event of a loss of power. In addition, the stored parameter can be examined to determine the state of the parameter. These and other advantages of the present invention will be obvious to those skilled in the art upon a reading of the following Detailed Description of the Invention together with the drawings.